## Abstract

We consider concurrent systems in which there is an unknown upper bound on memory access time. Such a model is inherently different from asynchronous model where no such bound exists, and also from timing-baaed models where such a bound exists and is known a priori. The appeal of our model lies in the fact that white it abstracts from implementation details, it is a better approximation of real concurrent systems compared to the asynchronous model. Furthermore, it is stronger than the asynchronous model enabling us to design algorithms for problems that are unsolvable in the asynchronous model. Two basic synchronization problems, consensus and mutual exclusion, are investigated in a shared memory environment that supports atomic registers. We show that Θ(Δ ,logΔ/loglogΔ ) is an upper and lower bound on the time complexity of any consensus algorithm, where A is the (unknown) upper bound on memory access time. For the mutual exclusion problem, we design an efficient algorithm that takes advantage of the fact that some upper bound on memory access time exists. The solutions for both problems are even more efficient in the absence of contention, in which case their time complexity is a con- Stant.

Original language | English |
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Title of host publication | Proceedings of the 26th Annual ACM Symposium on Theory of Computing, STOC 1994 |

Publisher | Association for Computing Machinery |

Pages | 800-809 |

Number of pages | 10 |

ISBN (Electronic) | 0897916638 |

DOIs | |

State | Published - 23 May 1994 |

Externally published | Yes |

Event | 26th Annual ACM Symposium on Theory of Computing, STOC 1994 - Montreal, Canada Duration: 23 May 1994 → 25 May 1994 |

### Publication series

Name | Proceedings of the Annual ACM Symposium on Theory of Computing |
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Volume | Part F129502 |

ISSN (Print) | 0737-8017 |

### Conference

Conference | 26th Annual ACM Symposium on Theory of Computing, STOC 1994 |
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Country/Territory | Canada |

City | Montreal |

Period | 23/05/94 → 25/05/94 |

### Bibliographical note

Publisher Copyright:© 1994 ACM.